AC-DC Power Supplies Are Shrinking

Power-supply design trends are clear and dramatic: additional features, improved efficiency, and smaller size for the same power ratings, for both battery-powered portable units as well as larger, line-powered ones. For the AC-DC supplies, these changes are due to multiple factors combining to yield these more-compact designs. Some of the factors are obvious, but others are not.

Start with the most apparent change, which is the use of smaller passive components. Vendors are shifting the basic resistor and capacitor footprint from 0805 size (2.0mm by 1.25mm) to 0603 (1.5mm by 0.8mm), and to an even-smaller 0402 size (1.0mm by 0.5mm). Diodes, as well, are also available in smaller packages. The use of larger parts was a holdover habit from previous generations of supplies. It made sense for vendors to continue using parts, which were fully known and characterized in their supply chain and inventory, and all of the same size.

The pressure to reduce supply size, along with the electronic industry's growing use of smaller parts in consumer products, has made them the body size of choice. The result is a significant reduction in required PC board space -- the change from 0805 to 0402 cuts a component's immediate footprint to 20 percent of its previous value -- and there are many such devices on a supply's PC board.

Changes in the supply magnetics (inductors and transformers) are also helping reduce size. Traditionally, these components have been the most complex “simple” passive ones in the supply's implementation, often custom-designed by the OEM to get precisely the desired and often subtle combination of primary- and secondary-tier parameter values (including inductance, DC resistance, size, form factor, winding type, insulation, orientation, volume, and cost).

In addition, supply designers are making better use of the available inductor volume. For example, they are reorienting the inductor to take advantage of the supply's available height-dimension headroom, in return for a smaller footprint.

On the active component side, the power semiconductors’ packaging has shrunk, primarily for the critical MOSFETs of the output. Chip-scale power MOSFETs such as the DirectFET from International Rectifier (where the metal enclosure covering the bare die is also the drain terminal) provide significantly more power capability, but in a smaller package. This has had a major impact on supply size, since the DirectFET has a 30 percent larger MOSFET die but with a 60 percent reduction in PC board footprint compared to the widely used D2Pak package. Compared to the D-Pak package, the DirectFET die can be 33 percent larger than the D-Pak package, yet its footprint is 54 percent smaller.

Power-supply size also involves the necessary concerns for thermal loads. To address this issue, engineers are making extensive use of thermal gap pads for more efficient heat transfer. Since this thermal material can be a significant part of the bill of materials (BOM) cost, the heat-sink structure has been redesigned to use less of the gap-pad material, thus cutting both cost and size.

But sarcasm and irony are so much fun :)I'm also very annoyed by products that don't work as they should and/or or difficult/impossible to repair. It makes you wonder why anyone ever bothered to make them in the first place.

Ann, sorry about that. I don't do much sarcasm, nor irony. Quite possibly I am way to serious about things.

I am quite critical of both laziness and stupidity, though. I do catch grief for that on occasions.

Really though, there are a whole lot of companies that appear to be successful that have products that are very challenging to even diagnose, let alone to service. Some of them get into the "made by monkeys" section of this fine publication, some don't.

Ann, there are a whole lot of products that are simply not worth repairing. Others aren definitely worth repairing and happen to be conveniently repairable. THAT did not just happen: designing for repairability is cloesly linked to designed for assembly. Only just a bit more effort.

But it also has an extra benefit, which is a design using components available from multiple sources. So that when I can't get parts frpom one maker, I can use parts from another maker. That is quite handy.

William, I agree. But apparently the math needed to figure that out is too complicated for some companies, or they are too short-sighted. In this case, one hardly needs 20/20 hindsight to come to your conclusion.

What I find is that to provide the quality in my product that justifies the price I need to use a power supply that is quite a bit more expensive than the cheapest one that would work. But the adequate margins abd better construction have meant that no failure have occured in ten years. That has been quite good for the products reputation. It IS INDEED cheaper to do things right the first time.

The standards electrical machines and components are required to meet in the food processing industry are far more stringent than those in traditional plant construction. For specialized production environments such as these, components must not only resist thermal and physical stresses, but they must also be resistant to the chemicals used to sterilize equipment.

The word “smart” is becoming the dumbest word around. It has been applied to almost every device and system in our homes. In addition to smartphones and smart meters, we now hear about smart clothing and smart shoes, smart lights, smart homes, smart buildings, and every trendy city today has its smart city project. Just because it has a computer inside and is connected to the Web, does not mean it is smart.

Was Steve Job’s signature outfit of a black turtleneck, jeans, and sneakers the secret behind his success? Maybe, or maybe not, but it was likely an indication of a decision-making philosophy that enabled him to become one of the most successful innovators of all time.

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